java - 程序由于递归而变慢

Question

我正在尝试编写一个程序，将 C: 驱动器上的每个文件和文件夹名称添加到 ArrayList。该代码工作正常，但由于大量的递归，它变得非常慢。这是代码:

public static void updateFileDataBase()
{
    ArrayList<String> currentFiles = new ArrayList<String>();
    addEverythingUnder("C:/",currentFiles,new String[]{"SteamApps","AppData"});
    for(String name : currentFiles)
        System.out.println(name);
}
private static void addEverythingUnder(String path, ArrayList<String> list, String[] exceptions)
{
    System.gc();
    System.out.println("searching " + path);
    File search = new File(path);
    try
    {
        for(int i = 0; i < search.list().length; i++)
        {
            boolean include = true;
            for(String exception : exceptions)
                if(search.list()[i].contains(exception))
                    include = false;
            if(include)
            {
                list.add(search.list()[i]);
                if(new File(path + "/" + search.list()[i]).isDirectory())
                {
                    addEverythingUnder(path + "/" + search.list()[i],list,exceptions);
                }
            }
        }
    }
    catch(Exception error)
    {
        System.out.println("ACCESS DENIED");
    }
}

我想知道是否可以采取任何措施来加快这一过程。预先感谢:)

Answer 1

Program slowing down due to recursion

不，不是。递归不会让事情变慢。糟糕的算法和糟糕的编码会让事情变慢。

例如，您正在为您处理的每个文件调用Files.list()四次，以及 每个目录一次。您可以通过对每个目录执行一次来节省 O(N):

   for(File file : search.listFiles())
    {
        String name = file.getName();
        boolean include = true;
        for(String exception : exceptions)
            if(name.contains(exception))
                include = false;
        if(include)
        {
            list.add(name);
            if(file.isDirectory())
            {
                addEverythingUnder(file,list,exceptions);
            }
        }
    }